This invention has to do with optical systems and more particularly to a laser optical focusing device.
In order to generate thermonuclear power by laser fusion, it is necessary to illuminate the fuel pellet, which is generally spherical and must be uniformly imploded to achieve the conditions necessary to ignite a fusion reaction. Thus, it is desirable to focus the laser beam substantially uniformly over the entire spherical surface of the fuel pellet and, in addition, it has been found desirable that the illumination be orthogonal to the fuel pellet surface to avoid refraction losses.
Further, it has been found to be desirable to divide the laser beam into a plurality of beams and to direct each beam toward the fuel pellet from a different angle. It has been known to use as many as nine beams, but such a system is fraught with difficulties due to the complexity and cost thereof.
In order to overcome the aforesaid problems, it has been proposed to employ an ellipsoidal mirror illumination system. Such a system is described by C. E. Thomas in an article entitled, "Laser Fusion Target Illumination System" appearing in the June 1975 issue of "Applied Optics", Vol. 14, No. 6. In the Thomas system two ellipsoidal mirrors are mounted in opposed relationship with the fuel pellet being placed therebetween. The second focus of each ellipsoid is designed to coincide with the wall of the opposing mirror so that a laser beam enters through a medial hole in each ellipsoid and reflects off the opposite ellipsoid onto the fuel pellet. While this system has been reasonably successful, the present invention is directed to improvements thereover, which will become apparent as the description proceeds.